Wavelength selective detectors are useful in wavelength-division multiplexing applications. By sending separate signals at different wavelengths through an optical fiber, and detecting these wavelengths separately, one can increase the information capacity of a communications system. The light sources could consist of semiconductor lasers or narrow-spectrum light emitting diodes (LEDs) such as a resonant cavity LED (RCLED). The detection system must be able to demultiplex the signal, i.e., detect the different wavelength signals separately. Each detector in the demultiplexing scheme must be able to detect the light from its design wavelength with good efficiency, while being insensitive to all other wavelengths in order to minimize cross-talk between channels.
Recently, resonant cavity enhanced (RCE) photodetectors have been studied for use in wavelength-division multiplexing applications. These designs place the absorbing region of a photodetector within a Fabry-Perot resonant cavity consisting of epitaxial semiconductor layers. Such devices can exhibit high speed, can have thin absorption regions, and detect light most strongly at the resonant wavelength of the cavity while reflecting non-resonant wavelengths. These devices, however, require the growth of a thick epitaxial distributed Bragg reflector (DBR) semiconductor mirror below and usually above the active region. For example, see K. Kishino et al., "Resonant Cavity--Enhanced (RCE) Photodetectors", IEEE Journal of Quantum Electronics, Vol. 27, No. 8, August 1991, pages 2025-2026.